Measuring Vegetation Health Investigation Using Remote Sensing Data : Spatial Aspects MODIS satellite image of New England

The Earth Observing satellites have different spatial views of Earth depending on the instrumentation of the satellite and what it’s purpose is. How many scenes an instrument can capture each orbit and how large it’s Earth footprint is will tell us about repeat-cycle and image resolution. IKONOS 1 meter resolution Fenway Park Landsat 30 meter resolution MODIS 500 meter resolution 3

We will look at images with which you may be familiar around Boston, Massachusetts. These images will be from three different satellites that are in orbit at least 250 miles above the earth. The satellite images have different resolutions. We will look at Fenway Park, Bunker Hill Monument, and Logan Airport. You will have an opportunity to zoom in and out of images. IKONOS satellite image September 6, 2000 Digital photograph courtesy of BaseballPilgrimages.com 2

Satellites have a footprint: the area on earth they cover for one scene. For MODIS, the footprint size is 10 degrees by 10 degrees, or about 1000 kilometers on a side. A MODIS footprint (blue box) is called a “tile”. A Landsat footprint is 185 km on a side. (See the white outline) About how many Landsat footprints are in a MODIS footprint? Landsat footprint 4

5 The smallest data “point” of a satellite image is called a pixel. A pixel is the smallest piece of a footprint. The word was created from a shortening of “picture element”. To scale, the blue outline represents one MODIS 500 m pixel, the yellow box would be one 30 m Landsat pixel, and the black square would be one 4m IKONOS pixel.

It is important to know how frequently a satellite will look at the same geographic area on Earth so we can compare images that are taken at different times. Because the Earth rotates beneath the satellite, the orbit shifts every 100 minutes, and takes a “snapshot” of Earth below it several times an orbit. The repeat-cycle is how long it takes the satellite to be aligned over the same area again. Repeat-cycle 6

The blue outline contains a 500m x 500 m area on this IKONOS image. The blue box represents one MODIS pixel. 7

IKONOS 1 m resolution 100 m box How does the yellow box compare with the distance from home to first base? 8

100 m box zoomed until pixels appear on IKONOS image The lower right corner has parked cars. About how long are they? 9

Zoom InScale Lake Champlain Do you see rivers or other geographic features on this slide? MODIS Sept 22, 2005 St Lawrence River Boston Cape Cod km

Zoom InZoom Out km MODIS Sept 22,

25 km.8 Zoom InZoom Out km MODIS Sept 22,

Zoom InZoom Out km MODIS Sept 22,

Zoom InZoom Out km MODIS Sept 22,

Next slideZoom Out km You can start to see individual pixels and Boston appears “out of focus”. MODIS Sept 22,

MODIS Sep m resolution Landsat ETM Sep m resolution 16 Cape Ann

9 km Landsat ETM+ September 27, 2000 Zoom InScale 0 12 km 17

Landsat ETM+ September 27, 2000 Zoom InZoom Out km 18

Zoom InZoom Out km Landsat ETM+ September 27,

Zoom InZoom Out km Landsat ETM+ September 27,

Zoom InZoom Out km 0 3 Landsat ETM+ September 27,

0 1 km Next slideZoom out 22

km m pixels1m pixels These two images are about the same scale, but Landsat is at the limit of its resolution. You will see the difference in detail when you zoom the 1m IKONOS image IKONOS images in spectral bands have 4 meter resolution. IKONOS panchromatic band (appears black and white) is 1 meter resolution. Here we will look at the panchromatic images to get the best resolution.